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Context: Although a monoallelic mutation in the calcium-sensing receptor ( CASR ) gene causes familial hypocalciuric hypercalcemia (FHH), the functional characterization of the identified CASR mutation linked to the clinical response to calcimimetics therapy is still limited., Objective: A 45-year-old male presenting with moderate hypercalcemia, hypocalciuria, and inappropriately high parathyroid hormone (PTH) had a good response to cinacalcet (total serum calcium (Ca 2+ ) from 12.5 to 10.1 mg/dl). We identified the genetic mutation and characterized the functional and pathophysiological mechanisms, and then linked the mutation to calcimimetics treatment in vitro ., Design: Sanger sequencing of the CASR , GNA11 , and AP2S1 genes was performed in his family. The simulation model was used to predict the function of the identified mutant. In vitro studies, including immunoblotting, immunofluorescence, a cycloheximide chase study, Calbryte™ 520 Ca 2+ detection, and half-maximal effective concentration (EC 50 ), were examined., Results: This proband was found to carry a de novo heterozygous missense I554N in the cysteine-rich domain of CASR , which was pathogenic based on the different software prediction models and ACGME criteria. The simulation model showed that CASR I554N mutation decreased its binding energy with Ca 2+ . Human CASR I554N mutation attenuated the stability of CASR protein, reduced the expression of p-ERK 1/2, and blunted the intracellular Ca 2+ response to gradient extracellular Ca 2+ (eCa 2+ ) concentration. The EC 50 study also demonstrated the correctable effect of calcimimetics on the function of the CASR I554N mutation., Conclusion: This novel CASR I554N mutation causing FHH attenuates CASR stability, its binding affinity with Ca 2+ , and the response to eCa 2+ corrected by therapeutic calcimimetics., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Lin, Ding, Huang, Chen, Lee, Sung and Lin.)

Introduction: Prenatal diagnosis of bone and mineralization anomalies is associated with a wide range of etiologies and prognoses. The improvement of antenatal ultrasound combined with the development of molecular diagnosis in genetics has transformed antenatal medicine into a challenging discipline. Of the various known causes of bone abnormalities and hypomineralization, calcium and phosphate metabolism disorders are exceptional. An accurate diagnosis is crucial for providing appropriate genetic counseling and medical follow-up after birth., Case: We report on three siblings with severe bone abnormalities diagnosed during the second trimester ultrasound of pregnancy. Postnatal follow-up showed transitory hyperparathyroidism, with hypercalcemia and hypocalciuria., Methods: Sanger sequencing performed after birth in the three newborns revealed a monoallelic pathogenic variant in the CASR gene, encoding the calcium sensing receptor, confirming the diagnosis of familial hypocalciuric hypercalcemia, paternally inherited. Postnatal evolution was favorable after treatment with a calcimimetic agent., Conclusions: Previously, prenatal bone abnormalities caused by familial hypocalciuric hypercalcemia had only been described in one patient. This entity should be considered as differential diagnosis of bones abnormalities. Knowing about this unusual etiology is important to guide the diagnosis, the prenatal counseling and to improve medical management., (© 2022 John Wiley & Sons Ltd.)

The calcium-sensing receptor (CaSR) is a G-protein-coupled receptor with a crucial role in calcium homeostasis. Mutations in the CaSR gene may lead to specific parathyroid disorders due to either gain-of-function (autosomal dominant hypercalciuric hypocalcemia; ADHH) or loss-of-function (familial hypocalciuric hypercalcemia; FHH). Our aim was to evaluate CaSR mutations as a cause of disease in selected patients. We identified and recruited patients with phenotypes suggestive of CaSR-related parathyroid disorders. DNA was extracted, and CaSR gene was sequenced. Live-ratiometric measurements of intracellular [Ca(2+)] and Western blot assays for evaluation of MAPK phosphorylation in response to changes in extracellular [Ca(2+)] were performed in transiently transfected HEK-293T cells to functionally characterize mutants. A total of 21 patients were evaluated, seven of them with idiopathic hypoparathyroidism (suspected ADHH) and 14 with hyperparathyroidism (suspected FHH). In the latter group two patients were found to harbor missense mutations: a novel heterozygous I32 V mutation in a female index case and a sporadic known R185Q mutation in a 1-year-old girl. In-vitro functional studies showed that I32 V is an inactivating mutation. In our study, most patients had normal CaSR sequencing. This suggests that phenotypic pitfalls may occur at time of patients' selection for CaSR sequencing. In one patient with strong positive pre-test probability based on both familial history and appropriate phenotype, a novel I32 V mutation leading to FHH was identified and characterized. In cases of familial parathyroid disorders, CaSR sequencing should be performed, but if negative, one should consider involvement of alternative genes or mechanisms.

Hypercalcaemia is rare in children. In adulthood, the causes are most frequently malignancy and primary hyperparathyroidism. In children, however, the aetiologies are diverse and age specific, and many have an underlying genetic basis. Hypercalcaemia is a serious condition that frequently leads to end-organ damage. In order to provide the most appropriate treatment, a key part of the management pathway is to establish the correct diagnosis promptly. When considering a practical approach to hypercalcaemia in children, it is helpful to consider the causes of hypercalcaemia according to the accompanying levels of parathyroid hormone (PTH), indicating whether the causes are PTH dependent or PTH independent. This chapter reviews the recent advances in this area and presents a practical approach to the investigation and subsequent management of this condition., (© 2015 S. Karger AG, Basel.)

The calcium-sensing receptor (CASR), a plasma membrane G-protein coupled receptor, is expressed in parathyroid gland and kidney, and controls systemic calcium homeostasis. Inactivating CASR mutations have previously been identified in patients with familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT). The aim of the present study is to determine the underlying molecular defect of FHH/NSHPT disease in a consanguineous Tunisian family. Mutation screening was carried out using RFLP-PCR and direct sequencing. We found that the proband is homozygous for a novel 15 bp deletion in the exon 7 (c.1952_1966del) confirming the diagnosis of NSHPT. All the FHH members were found to be heterozygous for the novel detected mutation. The mutation, p.S651_L655del, leads to the deletion of 5 codons in the second trans-membrane domain of the CASR which is thought to be involved in the processes of ligand-induced signaling. This alteration was associated with the evidence of mental retardation in the FHH carriers and appears to be a novel inactivating mutation in the CASR gene. Our findings provide additional support for the implication of CASR gene in the FHH/NSHPT pathogenesis.

Introduction: As primary hyperparathyroidism affects mainly middle-aged and elderly women, it is an infrequent finding during gestation and breastfeeding. To date, less than 200 pregnant patients with primary hyperparathyroidism diagnosed during pregnancy have been described. Like in other disorders of the parathyroid gland, the recognition of primary hyperparathyroidism during pregnancy and lactation may be difficult, as clinical symptoms are not specific, while laboratory findings may be masked by some typical pregnancy-induced changes in calcium and phosphate homeostasis. If remains untreated, the disease may result in serious clinical implications for the mother and fetus. Most authors consider surgery within the second trimester of pregnancy as the treatment of choice in this group of patients., Case Report: In our paper, we discuss the case of a 35-year-old female with a history of recurrent acute pancreatitis and recurrent abortions. As the patient declined surgery, conservative management with calcitonin was started and continued throughout the rest of pregnancy, and led to giving birth to the infant whose only health problem was transient hypocalcemia., Conclusion: The described case shows that conservative management, if started respectively early and conducted on the basis of a patient's condition, may effectively reduce increased perinatal and maternal morbidity and mortality in pregnant women declining surgery.

A loss of calcium-sensing receptor (CASR) function due to inactivating mutations can cause familial hypocalciuric hypercalcemia (FHH) or neonatal severe hyperparathyroidism (NSHPT). NSHPT represents the most severe expression of FHH and courses as a life-threatening condition. The aim of this study was to identify and characterize a CASR mutation in a female infant brought to the health service due to dehydration, apathy, lack of breast feeding and severe hypercalcemia. Molecular analysis was performed on genomic DNA of the index case and her parents. A novel homozygous mutation (p.E519X) in CASR was identified in the proband; both mother and father had the same mutation in heterozygous state, confirming their FHH condition. The mutation results in a truncated and inactive protein due to the lack of transmembrane and intracellular domains. The identification of this novel CASR gene mutation established the basis of hypercalcemia in this family and allowed a genetic counseling.

Neonatal severe hyperparathyroidism (NSHPT) is considered an autosomal-recessive disorder, attributable in many cases to homozygous inactivating mutations of the Ca++-sensing receptor (CASR) gene at 3q13.3-21. Most heterozygotes are clinically asymptomatic but manifest as familial (benign) hypocalciuric hypercalcemia (FHH) with a laboratory profile that is variably and sometimes only marginally different from normal. In 5 NSHPT cases from 3 Nova Scotian families, we found homoallelic homozygosity for an insertion mutation in exon 7 of CASR that includes an Alu repeat element with an exceptionally long polyA tract. Four of the 5 NSHPT infants were treated by parathyroidectomy more than a decade ago and are well now. A fifth went undiagnosed until adulthood and has profound musculoskeletal and neurobehavioral deficits. Among 36 identified FHH heterozygotes are 3 individuals with an unexpected degree of hypercalcemia and elevated circulating parathyroid hormone levels consistent with secondary hyperparathyroidism. Two are obligately heterozygous offspring of NSHPT mothers with surgical hypoparathyroidism and variable compliance with vitamin D therapy. The other is an adult with coexistent celiac disease in whom hyperparathyroidism, probably secondary to vitamin D deficiency, led to surgery. In counseling affected families, the heterozygous state should not be considered entirely benign, since FHH heterozygotes, particularly infants, may be prone to secondary hyperparathyroidism and symptomatic hypercalcemia. In such families, molecular diagnosis will allow for unambiguous identification of at-risk individuals.

A boy is described who presented aged 7 weeks with severe biochemical and radiological neonatal hyperparathyroidism that had completely resolved by the age of 6 months. His mother had a normal serum calcium concentration but his father, paternal aunt, and paternal cousin all had a raised serum calcium due to familial hypocalciuric hypercalcaemia.

A Japanese female neonate exhibiting severe respiratory distress was found to have primary hyperparathyroidism. Features included demineralization of the bones, hypercalcemia, hypophosphatemia, and elevated levels of parathyroid hormone, together with marked, generalized aminoaciduria. Four enlarged parathyroid glands were surgically removed, and remineralization of the bones was noticed after the operation. The characteristic pathologic change of the glands was chief cell hyperplasia. A survey of the family identified three other hypercalcemic but asymptomatic relatives. The mode of inheritance was autosomal dominant. This patient seems to be the second neonate with familial hypocalciuric hypercalcemia to be described in the literature.

We present a newborn baby with a diagnosis of neonatal severe primary hyperparathyroidism, based on the concomitant presence of hypercalcemia, hypophosphatemia and elevated values of parathormone. A national and international review on the subject is made and the differential diagnosis of this rare entity is discussed.